Radio aerial system



Dec. 16, 1952 J. F. RAMSAY ET AL 2,622,199

RADIO AERIAL SYSTEM Filed Oct. 11, I948 Patented Dec. 16,1952

RADIO AERIAL SYSTEM John Forrest Ramsay, Chelmsford, and John DewarPeat, Great Baddow, England, assignors to Marconis Wireless TelegraphCompany Limited, London, England, a company of Great Britain ApplicationOctober 11, 1948, Serial No. 53,806 In Great Britain April 16, 1948 7Claims.

This invention relates to radio aerial systems and more particularly tosuch systems incorporating dipole, unipole, half-wave, quarter-wave andsimilar aerial elements. For the sake of brevity in description dipoleaerial elements will be almost exclusively referred to in thisspecification but as will be apparent later the invention also appliesto systems incorporating unipole, quarter wave and like elements.

The electric field from a horizontal dipole contains a verticalcomponent of polarization except at points in a vertical planeperpendicular to the dipole axis through the center of the dipole wherethe field is purely horizontally polarized. The existence of verticalcomponents of polarization at points in space removed from this plane isa more or less serious disadvantage for many purposes; for example, withthe so-called omni-directional range beacon method of radio navigationit is very desirable that the vertical component shall be absent at allangles both as regards the omni-directional beam and the rotating beam.

The present invention seeks to provide improved aerial systems wherebythe vertical component of polarization in the field of a horizontaldipole or like aerial elements may be substantially eliminated. Thoughnot limited to its application thereto the invention is, therefore, ofparticular advantage when applied to the aerial systems of so-calledomni-directional range beacons.

According to this invention a dipole or like aerial element is mountedin a screen constituted by a tubular wave guide having its axissubstantially at right angles to the element axis and provided with aplurality of resonant slots cut in the wall of the tube substantiallyparallel to the axis thereof. The screen thus constituted issubstantially transparent to horizontal polarization and substantiallyopaque to vertical polarization with the result that the combination orthe aerial element and screen provides for practically completeelimination of the vertical component.

The invention is illustrated in the accompanying drawings which show twoembodiments in simplified schematic perspective. Like references areused for like parts in both figures.

Referring first to Fig. 1 a horizontal dipole I is mounted centrallywithin a tubular screen or wave guide 2 whose ends are closed byconductive plates 3, 4 and whose axis is vertical, said screen or waveguide being provided with equally spaced vertical slots 5 in itscircumferential wall each slot being about half of a wave length (infree space) long. The axial length of the wave guide is preferably abouthalf a wave length (in the wave guide) long, i. e. half a guided wavelength long.

screen. Such a combination of dipole I loop 6' The number and width ofthe slots may be varied within fairly wide limits and preferably, thoughnot necessarily, the horizontal dipole is substantially at the center ofthe vertical tubular radiating cavity constituted by the wave guide.

The dipole element excites an H mode as the dominant mode, the diameterof the tube 2 being so chosen that other modes-notably the E010mode--liable to be produced by vertical support provided for the dipoleare practically negligible. The slots are excited by the transversecurrents associated with the H111 mode, those on or near the dipole axisbeing extremely weakly excited While those on or near the perpendicularto the axis being fully excited. The radiation pattern in the horizontalplane thus tends to form a figure-of-eight with the axis of the eightperpendicular to the dipole axis. By rotating the dipole thefigure-oi-eight pattern may be rotated.

The vertical radiation pattern is substantially the magnetic planepattern of a magnetic dipole and is substantially uniform in allvertical planes as the electric dipole is rotated. The combinationrotating aerial element and wave guide screen may be regarded asequivalent to a cylindrical array of magnetic dipoles and accordinglythe solid radiation pattern is substantially free from verticallypolarized components.

The wave guide or screen is not of necessity half a guided wave lengthlong nor need the dipole element be centrally situated with regard tothe slots for itmay be above or below the ring of slots, the wave guideproper in that case being made longer. For example, the dipole elementmay be situated about a quarter of a guided wave length from the bottomor top plate of the guide proper (or from a transverse piston likeclosure member therein) and may excite a travelling H1 mode in the solidtubular guide. The distance between the dipole and the center of theslots may be varied within fairly wide limits but may conveniently beone half of a guided wave length.

If, as above set forth, the electric dipole is displaced with regard tothe slots, i. e. is beyond their ends, a p source of radiation may bearranged horizontally with its axis coinciding with the axis of thetubular wave guide, said loop being arranged in the horizontal planebisecting the lengths of the slots. Such an arrangement is shown in Fig.2 in which I is the dipole and 6 is the loop. Since the diameter of theguide tube 2 is below cut oil for the H0 mode the screen constitutedthereby will be purely reactive in nature. The radiation pattern of theloop 6 will therefore not be seriously affected by the presence of the 3and screen 2 constitutes a very advantageous structure for anomni-directional range beacon.

It will be noted that the invention enables two serious difiicultiesencountered with known aerial systems, of the, nature, in question to beavoided namely (1) that of obtaining bi-directional and omni-directionalaerial elements with identical zenithal polar diagrams and (2) that ofavoiding pattern distortion due to phase differences caused by thephysical separation of, thetwo aerial elements. These difficultiesareovercome because, in carrying out the present invention (1) the, twoaerial elements radiate identical zenithal polar diagrams and (2) theenergy from the said two elements is radiated from the same apparent,

point source.

As already stated, instead of using a dipole a unipole or like elementmay be employed,

What we claim is:

1. An aerial system including ahdipoleiand a loopradiatoraerial. elementmounted within a screen constituted by a tubular wave guide with itsaxis substantially perpendicular to the axis of said dipole andvparallel to the axis of said loop radiator, said guide havinga pluralityof resonant slots formed in, its wall with their lengths substantiallyparallel to the guide axis, said dipole being positioned in theunslotted length of said guide and, said loopradiator being mountedsubstantially in a plane bisecting the lengths of said slots.

2. An aerial system including a dipole and a loop radiator aerialelement mounted in a screen constitutedby a tubular wave guidewith itsaxis substantially perpendicular to the axis of said dipole andsubstantially parallel to the axislof saidloopradiator, said guide beingof substantiallytubular section and having a length of substantiallyhalf a guided'wave length, measured in the guide at the operatingfrequency and having aplurality of resonant slots each substantiallyhalf a wave length long, in free space, at the operating frequencyformed in its wallwith. their lengthssubstantially parallel to theguideaxis, and said dipole being positionedin the unslotted length of,said guide and, said, loop radiator being mounted substantially in aplane bisecting ,the lengthsof said slots.

3, Any omni directional radio beacon aerial system comprising incombination a linear aerial elementmounted withits, axis substantiallyhori: zo ntal in ascreen constituted by a substantially vertical tubularwave guidea loop aerial element,

mounted in said screen with its axis. substantially vertical, said guidehaving a plurality of narrow elongated substantially vertical, resonantslots formed in itswall said slots being of, equal length and disposedin a-singlerow and extending only along part of thelength of saidscreen, saidlinear aerial element being disposed within said screen anddisplaced'from the terminating ends of said resonant, slots wherebyradiated vertically polarized components of the electricv st tutedbra-su stantial y vertical tubules-waves guide having a tubular wallportion and a plurality of narrow elongated substantially verticalresonant slots formed in the wall portion, each substantially a halfwave length long, said slots being arranged with their directions oflength parallel to the axis of the guide and in the form of a ring ofslots extending around said guide, the lengths of said slots lying onthe surface of an imaginary cylinder which is co-axial with said guideand withinsaid guide, a linear aerial element having its axissubstantially horizontal and disposed Within the tubular wall portion ofsaid guide displaced from the ends of the slots therein,

a loop aerial element having its axis substantially verticalandrdisposed within the slotted portion oi'saidywaveguide, whereby theradiating vertically polarized components of the electric field from,said elements are substantially eliminated while horizontally polarizedcomponents are radiated; substantially without, loss by the energizationof, said, slots.

7. A radio beacon aerial system having a slotted guide comprising incombination a screen constituted byhasubstantially vertical tubular waveguide having a plurality of narrow elongated substantially verticalresonant slots formed in the wall portion-and an unslotted wall portion,each slot substantially a half wave length long, said slots beingarranged with their directions of length parallel to theaxisof theguideand in the form of a ring of slots. extending around said guide, thelengths of said slots lying on-the surface of .an imaginary cylinderwhich is oo-axial with said guide, and. withinsaid. guide, a rotatabledipole having its axis extending transversely of saidguide in saidunslotted portion of said guide remote from the terminating ends of saidslots, a horizontally disposed loop aerial in the slotted portion ofsaid guide in a plane half way between the, terminating ends of saidslots, whereby the radiatingvertically polarized components of theelectric field from said dipole and from said loop are substantiallyeliminated while horizontally polarized components are radiatedsubstantially without loss by the energization of said slots.

JOHN FORREST RAMSAY. .JOHN DETWARPEAT.

- REFERENCES CITED Thefollowing references are of record in the file of.this patent;

UNITED STATES; PATENTS Num er Na Date 2,407,068 Fiske et al Sept. 3,1946 2,414,266 'Lindenblad Jan. 14, 1947 2,415,094 Hansen et a1 Feb. 4,1947 2,432,990 Hansen Dec. 23, 1947 2,433,924 Riblet Jan. 6, 19482,460,286 Hansenvet al Feb. 1, 1949 2,465,416 Aram Mar. 29, 19492,482,162, Feldman Sept. 20, 1949 2,489,288 Hansen Nov. 29,1949

FOREIGN PATENTS Number Country Date 5383;665 France July'12, 1943 OTHERREFERENCES Riblet: Microwave Omnidirectional Antennas-.:"Proc. IRE, vol.35, May 1947, pages 4'74 to 478.

Benoit; Omnidirectional centimetre-Wave Aerial/I Proc.;IRE,,Abstr-actNo. 957. Vol.36, May lfififinpal fiififii

